MADI-Multichannel Audio Digital Interface
Expertise from Lab X Technologies is applied in
products like the FPGA -based MADIX module
utilized in the Avid Venue console line.While career comebacks and popularity resurgences are not uncommon in the music industry, such comebacks are unheard of in the realm of digital transports—that is, unless you’re former superstar MADI. No, it’s not the diminutive form of Madeline; instead a nearly 20-year technology, reappearing in modern technology at an ever increasing rate.
In 1991, the Multichannel Audio Digital Interface (MADI) was introduced by the Audio Engineering Society, hence its “official” standard name—AES10. While the original incarnation of standard AES10- 1991, defined 56 channels at 48 kHz with support varispeed (+/- 12.5 percent), it was later amended to support 64 channels at 48 kHz without support for varispeed. In 2003, the standard was amended to the current AES10-2003 “double rate” support for 32 channels of 96 kHz audio.
MADI was originally conceived to route digital audio through broadcast facilities via commonly available 75 coaxial cabling utilized for video distribution, where the typical MADI physical media is coaxial cable connected at the device via BNC connectors. For longer distances and electrical isolation, fiber-optic connections are often found. While MADI is unidirectional, i.e., data flows in only one direction, it is very common to find TX (transmit) and RX (receive) connectors to provide up to 64 x 64 channels via two coaxial or fiber-optic cables on a single device. MADI is a selfclocking protocol, meaning its clock is embedded in the data and does not separate clock and data lines.
Given MADI’s genesis from the AES, there are also many similarities to twochannel digital transport commonly called AES/EBU (technically AES3, created in 1985), thus 28 or 32 AES3 streams can be easily transported via MADI.
The widespread adoption of digital mixing consoles has further driven the digital audio industry and has certainly elevated the need for a convenient medium for point-to-point connections of large quantities of digital audio signals. MADI’s 64-channel capability fits the needs of small- to medium-scale consoles. Additionally, its support for both copper (coax) and fiber connections provides solutions for integration into broadcast facilities (via coax), as well as long-distance options via fiber. This, coupled with a new generation of lower-cost MADI devices from the likes of RME and other manufacturers, effectively brought new life to what once was considered a dying standard.
MADI is inherently point-to-point. This is a blessing and a curse. The simplicity of connecting an RX to a TX is powerful and very similar to point-to-point conventional analog audio wiring. The downside is it can be costly to perform “splits,” sending the signal to multiple locations simultaneously, routing particular channels to various locations, or “merge” or combine channels from various MADI input devices into a single MADI stream. This requires additional MADI devices called routers and mergers, respectively, often specialized and quite expensive pieces of equipment. Additionally, MADI is not a network like Ethernet-based standards such as Audio Video Bridging (AVB) whereby the transport medium is inherently multipoint and routable (in the case of AVB by configuring routing through the Ethernet switches).
When using MADI, it is important to be aware of the non-standard mechanisms for transmitting device control data. While AES10 clearly defines audio data format for standardized inter-device communication, there is an additional “side channel” of data available. Various manufacturers have implemented non-standardized uses of the data, such as proprietary control of microphone preamps. Thus, utilization of such control capabilities may vary between manufacturers’ equipment.
The simplicity of point-to-point connections coupled with the high audio channel count capabilities will continue to make MADI an important part of the digital audio world for years to come. From near extinction to prominence…in that sense, MADI is the comeback king!
Lee Minich is president of digital connectivity specialist firm Lab X Technologies.
Lab X Technologies
Nothing demonstrates that MADI is alive and kicking better than a long list of current MADI adoptees. Companies like LabX Technologies and those on the following list are among the manufacturers building MADI interfaces, new lower-cost routers and mergers, and MADI-capable workstations and consoles.
Allen & Heath
Lynx Studio Technology
Roland System Group (RSG)
SSL (Solid State Logic)
Salzbrenner Stagetec Mediagroup